Double pulsed mixer-settler liquid-liquid extraction system



4 Dec. 26, 1967 R. E. M HENRY ETAL 3,360,340 DOUBLE PULSED MIXER-SETTLER LIQUID-LIQUID EXTRACTION SYSTEM I Filed Jan. 12, 1965 INVENTORS. Raymond ,5. Mc Henry John C. Posey ATTORNEY.

United States Patent DOUBLE PULSED MIXER-SETTLER LIQUID- LIQUID EXTRACTION SYSTEM Raymond E. McHenry, Oak Ridge, and John C. Posey,

Knoxville, Tenn., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Jan. 12, 1965, Ser. No. 425,093

3 Claims. (Cl. 23-2705) Our invention relates in general to liquid-liquid extraction systems and more particularly to such systems comprising a plurality of mixer-settlers.

Mixer-settlers are generally useful in carrying out liquid-liquid extraction processes, and, because of the simplicity of their construction and maintenance, are particularly useful in carrying out these processes in remote, shielded areas used for separating radioactive isotopes.

For eflicient operation two immiscible liquids separated in a settler must each leave only through its own outlet. To achieve this the interface between the two immiscible liquids must be maintained Within the zone between the outlet for the heavy phase and the outlet for the light phase. Problems arise in attempting to keep the interface at any desired point since its position changes with alterations in flow rates and densities of the two phases. Control of the interface position can be achieved by use of a pump; however, in remote cell operations, such as in processing radioactive isotopes, a system with no moving parts within the cell is preferred.

It is accordingly one object of our invention to provide an improved liquid-liquid extraction system.

It is another object to provide a mixer-settler system having improved interface control means.

It is still another object to provide a mixer-settler system having no moving parts in contact with the liquids being mixed and separated.

Othe objects of our invention will become apparent from the following detailed description and claims.

In accordance with our invention we have provided, in a mixer-settler system for contacting and separating two immiscible liquids having different densities comprising a plurality of interconnected mixer-settlers, a mixer-settler unit comprising: a vertically disposed elongated mixing vessel having an upper zone, a lower zone, and an intermediate zone; light fluid inlet means in said upper zone, heavy fluid inlet means in said lower zone, gas pulsing means communicating with said intermediate zone, and mixed fluid outlet means in said intermediate zone; an elongated settling vessel angularly disposed with respect to and in hydraulic communication with said mixing vessel, said settling vessel having an upper zone provided with light fluid outlet means, a lower zone provided with mixed fluid inlet means in hydraulic communication with said fluid outlet means in said mixing vessel.

High stage eificiency and excellent control of the interface level can be achieved with our system; yet no pumps are required within the mixer-settlers to move or mix the liquids. In the mixing the two immiscible liquids the pulsing means lifts the more dense liquid into the lighter liquid, thereby developing a head suflicient to drive the mixture of liquids from the mixer into the settler.

The figure is a diagrammatic representation of one embodiment of our invention.

In the figure the system comprises three identical stages. The mixers for these stages comprise column heads 1, 8 and 15; mixing columns 2, 9 and 16; column feet 3, 10 and 17; lower pulse inlet tubes 5, 12 and 19; upper pulse inlet tubes 4, 11 and 1S; and mixed phase outlet ports 6, 13 and 20. The settlers comprise slanting vessels 7, 14 and 21, each having mixed phase inlet ports in hydraulic communication with its associated mixer. Each settler is in hydraulic communication at its top with the head of the mixer of the next adjacent stage and at its bottom with the column foot of the mixer of the next preceding stage.

The sloping settlers provides the advantage of a rapid coalescence of the droplets of the discontinuous phase. Coalescence takes place principally when the droplets are impeded in their movement. Assuming the light phase is discontinuous, in a vertical settler this occurs when the droplets reach the top of the settler and in a sloping settler coalescence occurs when the droplets reach the upper sloping surface of the settler. The coalescence is further improved by providing a settler having a cross section which forces the droplets together as they move. A circular, elliptical, or a properly oriented rectangular or triangular cross section will achieve this result.

The angle at which the settlers are disposed with respect to the mixers is not critical, but is ordinarily dependent upon the spacing of the mixers and the mixer heights. An angle of 30 to 60 degrees from the vertical is preferred. Fluid outlet ports for all vessels must be at substantially the same elevation in order to maintain proper control of fluid flow. While not necessary, for ease in construction and operation it is preferred that the stages be identical with respect to each other.

The mixer and settler may be of any size, the dimension depending upon desired flow rates.

The pulse inlet means define the limits of the mixed phase zone. Therefore, one inlet must be above and the other below the mixed phase outlet port. A suitable spacing for the inlet ports is from 0.5 to 10 column diameters apart and the preferred spacing is from 1 to 5 column diameters apart.

The pulses introduced into the bottom and top of the mixer should be out of phase, and are preferably the same for all mixers. In order to simplify construction and operation of the system we prefer to have pulses introduced into the tops of all the mixers from one manifold and the pulses introduced into the bottoms of the mixers from another manifold. The pulse rate and amplitude are thus identical for all mixers. The liquid level in a mixer is not altered by the pulsing action.

The pulse rate and amplitude are not critical and values are preferred which provide good mixing with a minimum production of stable emulsion.

Flow rates are dependent upon the difference in densities of the two immiscible liquids, the viscosities of the mixed and aqueous phases, and the geometry of the ports.

I-laving thus described our invention in general, the following example is offered to illustrate it in detail.

Example A five-stage glass mixer-settler system was constructed in accordance with the figure. The inlets of the pulse tubes for each mixer were located about 9 centimeters apart and the outlet ports, having a diameter of about 1.6 centimeters, were positioned about halfway between these inlet ports. The diameter of the mixers was about 3.5 centimeters. The settlers, having a diameter of about 2.5 centimeters, were disposed at an angle of about 45 degrees to the vertical.

Tests were made of this system by introducing an aqueous phase comprising one molar nitric acid and europium isotopes at a flow rate of 1.6 liters per hour into the system countercurrent to an organic solution of 40 percent di-Z-ethylhexyl phosphoric acid in a kerosene-type diluent. The organic flow rate was 1.85 liters per hour. The pulse rate was about 60 per minute and the pulse volume was about 15 milliliters (about 10 percent of the mixer volume). The pulses introduced into the tops of the mixers were degrees out of phase with the pulses introduced into the bottoms of the mixers. Analyses were made of the europium concentration in the aqueous organic phase in each mixer and settler. The average stage efficiency was over 96 percent. This indicates that the back mixing was low and equilibrium was nearly attained in all stages.

The foregoing example is intended to illustrate, not limit, our invention. For instance, it is obvious that changes may be made in size and relative dimension of the vessels without departing from our invention.

Having thus described our invention, we claim:

1. In a mixer-settler system for contacting and separating two immiscible liquids having difierent densities comprising a plurality of interconnected mixer-settlers, a mixer-settler unit comprising:

(a) a vertically disposed elongated mixing vessel having an upper zone, an intermediate zone, and a lower zone, light liquid inlet means in said upper zone, heavy liquid inlet means in said lower zone, first and second gas pulsing means in said upper and lower zones, respectively disposed to introduce pulses toward and communicating with said intermediate zone for intermixing said liquids, and mixed fluid outlet means in said intermediate zone; and

(b) an elongated settling vessel angularly disposed to said mixing vessel at an angle of 30 to 60 degrees from vertical, and said settling vessel having an up per zone provided with light fluid outlet means, a lower zone provided with heavy fluid outlet means, and an intermediate zone provided with mixed fluid inlet means in hydraulic communication with the mixed fluid outlet means in said mixing vessel.

2. The system of claim 1 wherein said first mand second pulse inlet means are disposed apart a distance of about 0.5 to 10 times the diameter of said mixing vessel.

3. The system of claim 1 wherein said first and second pulse inlet means are disposed apart a distance of about 1 to 5 times the diameter of said mixing vessel.

References Cited UNITED STATES PATENTS 2,610,836 9/1952 Clarke 23270.5 X 2,629,654 2/1953 Olney 1- 23-267 X 2,646,346 7/1953 Coplan 23270.5 2,729,550 1/1956 Maycock 23267 X 2,754,179 7/1956 Whatley 23270.5 3,174,832 3/1965 Bohrer 23--267 X FOREIGN PATENTS 656,949 1/ 1963 Canada.

NORMAN YUDKOFF, Primary Examiner.

S. J. EMERY, Assistant Examiner. 

1. IN A MIXER-SETTLER SYSTEM FOR CONTACTING AND SEPARATING TWO IMMISCIBLE LIQUIDS HAVING DIFFERENT DENSITIES COMPRISING A PLURALITY OF INTERCONNECTED MIXER-SETTLERS, A MIXER-SETTLER UNIT COMPRISING: (A) A VERTICALLY DISPOSED ELONGATED MIXING VESSEL HAVING AN UPPER ZONE, AN INTERMEDIATE ZONE, AND A LOWER ZONE, LIGHT LIQUID INLET MEANS IN SAID UPPER ZONE, HEAVY LIQUID INLET MEANS IN SAID LOWER ZONE, FIRST AND SECOND GAS PULSING MEANS IN SAID UPPER AND LOWER ZONES, RESPECTIVELY DISPOSED TO INTRODUCE PULSES TOWARD AND COMMUNICATING WITH SAID INTERMEDIATE ZONE FOR INTERMIXING SAID LIQUIDS, AND MIXED FLUID OUTLET MEANS IN SAID INTERMEDIATE ZONE; AND (B) AN ELONGATED SETTLING VESSEL ANGULARLY DISPOSED TO SAID MIXING VESSEL AT AN ANGLE OF 30 TO 60 DEGREES FROM VERTICAL, AND SAID SETTLING VESSEL HAVING AN UPPER ZONE PROVIDED WITH LIGHT FLUID OUTLET MEANS, A LOWER ZONE PROVIDED WITH HEAVY FLUID OUTLET MEANS, AND AN INTERMEDIATE ZONE PROVIDED WITH MIXED FLUID INLET MEANS IN HYDRAULIC COMMUNICATION WITH THE MIXED FLUID OUTLET MEANS IN SAID MIXING VESSEL. 